net: add sysfs helpers for netdev_adjacent logic

They clean up the code a bit and can be used further.

CC: Ding Tianhong <dingtianhong@huawei.com>
CC: "David S. Miller" <davem@davemloft.net>
CC: Eric Dumazet <edumazet@google.com>
CC: Nicolas Dichtel <nicolas.dichtel@6wind.com>
CC: Cong Wang <amwang@redhat.com>
Signed-off-by: Veaceslav Falico <vfalico@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -4623,13 +4623,36 @@ struct net_device *netdev_master_upper_dev_get_rcu(struct net_device *dev)
 }
 EXPORT_SYMBOL(netdev_master_upper_dev_get_rcu);
 
+int netdev_adjacent_sysfs_add(struct net_device *dev,
+			      struct net_device *adj_dev,
+			      struct list_head *dev_list)
+{
+	char linkname[IFNAMSIZ+7];
+	sprintf(linkname, dev_list == &dev->adj_list.upper ?
+		"upper_%s" : "lower_%s", adj_dev->name);
+	return sysfs_create_link(&(dev->dev.kobj), &(adj_dev->dev.kobj),
+				 linkname);
+}
+void netdev_adjacent_sysfs_del(struct net_device *dev,
+			       char *name,
+			       struct list_head *dev_list)
+{
+	char linkname[IFNAMSIZ+7];
+	sprintf(linkname, dev_list == &dev->adj_list.upper ?
+		"upper_%s" : "lower_%s", name);
+	sysfs_remove_link(&(dev->dev.kobj), linkname);
+}
+
+#define netdev_adjacent_is_neigh_list(dev, dev_list) \
+		(dev_list == &dev->adj_list.upper || \
+		 dev_list == &dev->adj_list.lower)
+
 static int __netdev_adjacent_dev_insert(struct net_device *dev,
 					struct net_device *adj_dev,
 					struct list_head *dev_list,
 					void *private, bool master)
 {
 	struct netdev_adjacent *adj;
-	char linkname[IFNAMSIZ+7];
 	int ret;
 
 	adj = __netdev_find_adj(dev, adj_dev, dev_list);
@@ -4652,16 +4675,8 @@ static int __netdev_adjacent_dev_insert(struct net_device *dev,
 	pr_debug("dev_hold for %s, because of link added from %s to %s\n",
 		 adj_dev->name, dev->name, adj_dev->name);
 
-	if (dev_list == &dev->adj_list.lower) {
-		sprintf(linkname, "lower_%s", adj_dev->name);
-		ret = sysfs_create_link(&(dev->dev.kobj),
-					&(adj_dev->dev.kobj), linkname);
-		if (ret)
-			goto free_adj;
-	} else if (dev_list == &dev->adj_list.upper) {
-		sprintf(linkname, "upper_%s", adj_dev->name);
-		ret = sysfs_create_link(&(dev->dev.kobj),
-					&(adj_dev->dev.kobj), linkname);
+	if (netdev_adjacent_is_neigh_list(dev, dev_list)) {
+		ret = netdev_adjacent_sysfs_add(dev, adj_dev, dev_list);
 		if (ret)
 			goto free_adj;
 	}
@@ -4681,14 +4696,8 @@ static int __netdev_adjacent_dev_insert(struct net_device *dev,
 	return 0;
 
 remove_symlinks:
-	if (dev_list == &dev->adj_list.lower) {
-		sprintf(linkname, "lower_%s", adj_dev->name);
-		sysfs_remove_link(&(dev->dev.kobj), linkname);
-	} else if (dev_list == &dev->adj_list.upper) {
-		sprintf(linkname, "upper_%s", adj_dev->name);
-		sysfs_remove_link(&(dev->dev.kobj), linkname);
-	}
-
+	if (netdev_adjacent_is_neigh_list(dev, dev_list))
+		netdev_adjacent_sysfs_del(dev, adj_dev->name, dev_list);
 free_adj:
 	kfree(adj);
 	dev_put(adj_dev);
@@ -4701,7 +4710,6 @@ static void __netdev_adjacent_dev_remove(struct net_device *dev,
 					 struct list_head *dev_list)
 {
 	struct netdev_adjacent *adj;
-	char linkname[IFNAMSIZ+7];
 
 	adj = __netdev_find_adj(dev, adj_dev, dev_list);
 
@@ -4721,13 +4729,8 @@ static void __netdev_adjacent_dev_remove(struct net_device *dev,
 	if (adj->master)
 		sysfs_remove_link(&(dev->dev.kobj), "master");
 
-	if (dev_list == &dev->adj_list.lower) {
-		sprintf(linkname, "lower_%s", adj_dev->name);
-		sysfs_remove_link(&(dev->dev.kobj), linkname);
-	} else if (dev_list == &dev->adj_list.upper) {
-		sprintf(linkname, "upper_%s", adj_dev->name);
-		sysfs_remove_link(&(dev->dev.kobj), linkname);
-	}
+	if (netdev_adjacent_is_neigh_list(dev, dev_list))
+		netdev_adjacent_sysfs_del(dev, adj_dev->name, dev_list);
 
 	list_del_rcu(&adj->list);
 	pr_debug("dev_put for %s, because link removed from %s to %s\n",